1. Technical Field
The present invention relates generally to the field of identification systems, and more particularly to a hybrid ultrasonic and radio frequency identification system and method.
2. Description of the Related Art
Radio frequency identification (RFID) is a common means for identifying and providing information about articles. An RFID system includes a reader device and an RFID tag. RFID readers are typically handheld devices. Some cellular telephones include RFID readers. RFID readers direct signals at the RFID tag and receive and decode signals received from the RFID tag.
RFID tags are typically small flat devices that are affixed to the articles they identify. Despite their small size, current RFID tags are relatively complicated devices. Most RFID tags include an integrated circuit and an antenna. The integrated circuit includes memory for storing information, a small processor, and circuitry for modulating and demodulating a radio frequency signal. The antenna receives and transmits signals.
RFID tags may be passive, active, or semi-passive. Passive RFID tags have no internal power supply. Rather, a passive RFID tags is powered by a small current induced in its antenna by the signal transmitted by the RFID reader. Most passive tags signal by backscattering the carrier wave from the reader. An active RFID tags has an internal power source that it uses to power its integrated circuit and to broadcast a response signal to the reader. Active RFID tags tend to be more reliable than passive RFID tags. Semi-passive RFID tags are similar to active tags in that they have their own power sources, but the power source is used only to power the integrated circuit and not to power the broadcast response signal. The response signal is powered by backscattering the radio frequency energy from the reader.